화학공학소재연구정보센터
Chemical Engineering Science, Vol.56, No.15, 4627-4641, 2001
A theoretical and experimental investigation of reservoir-fed, rigid-roll coating
An industrially-important variant of reverse roll coating is studied in which the metering gap sits beneath a large, liquid reservoir, the influence of which is investigated via complimentary experimental, analytical (lubrication) and computational (finite element) methods, and for which gravitational effects are shown to be influential. Experimental measurements for both the flow rate and wetting line position are given over a wide range of roll speed ratio and capillary number and it is shown that, provided the wetting line is sufficiently far from the nip, the flow rate depends linearly on the reservoir level. A key feature of the mathematical models is that, unlike previous reverse roll coating studies. the variation of dynamic contact angle with metering roll speed has been accounted for. The lubrication model also uses boundary conditions which incorporate free surface, Surface tension and wetting line effects and the predictions from both models are found to be in generally good agreement with experiment. Finally, streamlines obtained from Finite Element solutions of the flow in the reservoir and wetting line regions are found to compare wall with corresponding experimental flow visualisations. The flow in the reservoir is recirculating in nature, the size and number of recirculations depending on the reservoir geometry.